4. C Programming

Question 1

Sort the following features according to if they are a feature of Java or a feature of C:

• object-oriented
• compiled into byte code
• compiled into an executable
• interpreted
• run-time errors are caught
• garbage collection
• choice between static and dynamic allocation
• solely dynamic allocation
• pointers
• explicit boolean and string type

Answer 1

• object-oriented: Java
• compiled into byte code: Java
• compiled into an executable: C
• interpreted: Java
• run-time errors are caught: Java
• garbage collection: Java
• choice between static and dynamic allocation: C
• solely dynamic allocation: Java
• pointers: C
• explicit boolean and string type: Java

Question 2

In
struct point { int x; int y; } p1;
what does p1 do?

Answer 2

Creates an instance of p1 (of structure type point)

Question 3

What operator accesses an attribute of a structure?

Answer 3

.

Question 4

What predefined function returns the total size of an instance of a structure?

Answer 4

sizeof()

Question 5

Take
struct point { int x; int y; } p1;

Then, p1 is set to (4, 5).
What does p1.y now translate to in MIPS?

Answer 5

Assume the base address of p1 is stored in $s0. Then, lw $t0, 4($s0)

Question 6

What is the difference between a structure and a type definition?

Answer 6

A structure is a defined collection of attributes about a thing. A type definition is a association between the name of the user-defined type and the structure itself:

typedef struct point point or typedef unsigned char byte

Question 7

How would you declare the array [3, 4, 5]?

Answer 7

int arr[] = {3, 4, 5};

Question 8

How would you declare an array of size 4 by 5?

Answer 8

int arr[4][5];

Question 9

How are strings ‘defined’ in C?

Answer 9

They are arrays of chars via ASCII. They end with \0, the null character.

Technically, you could officially define them by:

typedef char string[];

Question 10

What string functions do the following:
- assignment
- get length
- comparison

Answer 10

• strcpy (strcpy(s, "string"); )
• strlen (strlen(s))
• strcmp (strcmp(s1, s2))

Question 11

What is a pointer?

Answer 11

A variable that holds the address of a piece of data.

Question 12

What do each of these lines of code do?

int *p;
p = &i;
*p = 5;

Answer 12

1. Creates an pointer that can point to an integer.
2. p is set to the address of variable i
3. The value of i is set to 5.

Question 13

How are arguments passed to a function?

Answer 13

By value.

Question 14

Write a function that takes in two integer addresses and swaps their contents.

Answer 14

void swap(int* a, int* b) {
     int temp = *a;
     *a  = *b;
     *b = temp;
}

Question 15

Adding one to a pointer adds ____ to the address.

Answer 15

The size of the data type.

Question 16

What do the following commands do?

*p++;
*++p;
(*p)++;

Answer 16

1. Uses the value, and then increment the pointer.
2. Increment the pointer, then use the value;
3. Increase the value.

Question 17

What will the following code produce:

int* p = NULL;
*p;

Answer 17

A crash.

Question 18

What line will allocate dynamic space for n integers?
What frees the space?

Answer 18

int *p = malloc(n*sizeof(int));
free(p);

Question 19

What are the three areas of memory used for program variables?

Answer 19

Heap (dynamic allocation), Static (static/global variables) and Stack (local variables)

Question 20

Order the stack, static, instructions and heap by proximity to top of memory.

Answer 20

Stack ->, <- heap, static, instructions.